Global warming is projected to have immense effects on freshwater and wetland ecosystems, according to a report by a team of scientists led by a biologist from Colorado State University.

The climate change, which many researchers believe to be inevitable, could be devastating to trout, salmon and several species of aquatic plants and animals.

In a report titled "Aquatic Ecosystems and Global Climate Change," researchers forecast substantial shifts in fish habitats, decreasing water quality and disappearing wetlands. According to the study, rivers, lakes and wetlands may be seriously affected by the predicted global warming trend.

The report, which includes a review of more than 150 scientific studies, was released recently by the Pew Center on Global Climate Change. Its authors, freshwater biologist N. LeRoy Poff of Colorado State University, wetlands biologist Mark Brinson of East Carolina University and estuarine biologist John Day Jr. of Louisiana State University, said that increased temperatures forecast for the United States over the next century will disrupt animal and plant distributions and potentially threaten water quality throughout the nation.

"Wetlands and aquatic ecosystems are quite vulnerable to climate change," Poff said. "Projected increases in the earth's surface temperature due to global warming are expected to significantly disrupt current patterns of aquatic plant and animal distribution and to alter fundamental ecosystem processes, resulting in major ecological changes."

In particular, cold-water fish such as trout and salmon are projected to suffer substantially and disappear from large areas of their current geographic range. Some species attempting to flee warmer waters by migrating north or to higher elevations may become extinct due to natural or man-made barriers blocking their routes.

Conversely, fish that thrive in warm-water environments, including large mouth bass and carp, will potentially expand their ranges throughout the United States and Canada. A 4-degree rise in surface temperature would cause aquatic species to migrate 400 miles northward to maintain the same thermal habitat conditions as present.

According to the report, water quality will likely decline greatly due to expected reduction in summertime runoff and elevated temperatures. Additionally, warmer waters will likely increase the amount of blue-green and other nuisance algae that can reduce the amount of dissolved oxygen in the water.

According to Poff, reduced oxygen in lake waters due to increased production of algae could lead to the loss of large predatory fish and have negative effects on the food chain.

Poff noted that climate change could have other subtle effects on aquatic ecosystems as precipitation patterns change. In the coming century, areas accustomed to snow may instead get rain in the winter, causing floods that destroy fish eggs left in streams and leaving little snow pack to sustain rivers during the dry summer months.

The authors of the Pew Report said that the exact effects of global warming are impossible to predict because neither the specific temperature changes that might occur nor the effect such changes would have on precipitation levels can be known with certainty. However, the authors concluded that, in the face of inevitable climate change, humans can take actions to minimize the risk of ecosystem disruption.

The report is the seventh commissioned by the Pew Center, which was formed in 1998 to conduct studies and work with businesses on market-oriented ways to reduce greenhouse gases.